Porta Potties for Weddings, Festivals and Job Sites
The ratios are easy to look up and easy to misapply. What follows is six ordinary jobs worked through end to end, because the mistakes happen in the applying rather than in the arithmetic. If you just want the number, the calculator does it in one screen.
The two rules everything below rests on
For an event, one unit per 50 guests over four hours, from ANSI/PSAI Z4.3. Add 15 to 20% where alcohol is served, and go up with duration rather than treating eight hours like four. For a job site the number is law rather than guidance: 29 CFR 1926.51(c) sets one toilet up to 20 workers, then one seat and one urinal per 40, and per 50 above 200 workers.
Everything else here is those two rules meeting a real site. Run your own numbers.
A 150-guest wedding, six hours, drinks served
The base figure is three units. Six hours rather than four pushes it up, and alcohol adds another 15 to 20%, so four is the sensible order. One of those should be accessible, and a hand-wash station goes alongside because food is served.
The judgement call is what kind of unit. A standard cabin behind a tent at a farm venue is fine; at a formal reception it is the thing people remember. That is what restroom trailers exist for, and a two-station trailer covers roughly what three or four standard units cover over a short event, so the count from the ratio is not the count you order once you switch. Ask the supplier what their trailer is rated for.
A 40-worker site running four months
The federal floor is two toilets. Four months means weekly servicing on each, and over that period the servicing costs more than the rental, which is the line item people forget to compare. If the crew is spread across the site, two units at opposite ends beat two side by side for the same money, because walking time is the real cost.
Order a hand-wash station too. It is rarely required and always appreciated, and it is cheap against the day rate of the people using it.
A 2,000-person festival over two days
Count attendance, not tickets. A festival with 2,000 tickets across a weekend does not have 2,000 people on site at once, and sizing for the ticket number buys units that stand empty. Size for peak concurrent attendance, which for most multi-day events is well under the headline figure.
At this scale, split the units across at least three locations rather than banking them at one end, add urinal banks to take pressure off the cabins, and budget for servicing during the event rather than only between days. A unit handles roughly 200 to 250 uses before it needs attention, and a festival cabin hits that inside a day.
A 5,000-runner road race
Races break the ratio because the demand arrives as a spike in the ninety minutes before the gun rather than spread across the day. Size the start line for the peak rather than the average, which in practice means considerably more than one per 50, and then far fewer along the course and at the finish.
This is the one case where over-ordering at a single point is the right call. Runners queue at the start whatever you do; the question is whether the queue is five minutes or thirty.
A one-day county fair with food stalls
Food is what changes this one. Hand-wash provision moves from courtesy to expectation at roughly one station per four units, and it is ordered separately from the restrooms, which is why it is the line most often missing from a quote. Ask for it explicitly rather than assuming it comes attached.
Site the units away from the food, keep them on the accessible route, and remember that a fair runs long enough that mid-day servicing is worth pricing.
A rural site 40 miles from the nearest yard
Distance changes the economics more than the count. Delivery is priced off the drive from the yard to you, so a remote site pays more per unit and a mid-rental service visit costs the supplier a whole morning. Two consequences follow: order slightly more capacity than the ratio suggests so you are not calling for an emergency visit, and ask what the service interval will realistically be rather than what it is on paper.
Find the independent yards nearest your site before assuming the nearest one is the one that showed up in search.
What people get wrong
Counting tickets rather than attendance. The single most expensive error on this page, and the easiest to avoid.
Forgetting staff, crew and vendors. They are on site longer than the guests and they are almost never in the headcount somebody gives the supplier.
Treating duration as a rounding error. The same crowd over eight hours needs meaningfully more capacity than over four, and the ratio table says so plainly.
Adding the accessible unit last. It is the scarcest thing in most fleets on a summer weekend, so it is the one to book first. What actually makes a unit accessible.
Common questions
How many porta potties for 100 guests?
How many toilets does OSHA require on a job site?
How many ADA units do I need?
Figures on this page come from the Porta Potty Finder. How the data is collected.